Chain saws used for cutting of timbers and others have a main body, a guide bar extending from the main body, and a saw chain provided over the main body and the guide bar. A rear end side of the saw chain is wound around a sprocket provided in the main body, and when the sprocket is driven to rotate, the saw chain turns along an outer peripheral part of the guide bar.
Some of the chains saws described above are provided with an adjustment mechanism for adjusting the tension of the saw chain. Patent Literature 1 describes an adjustment mechanism including: a moving member which is coupled to a chain guiding plate corresponding to the above-described guide bar and is moved along a threaded rod member by rotation of the threaded rod member; a driven gear integrated with the threaded rod member; a driving gear provided in an operation part rotated by an operator; and an intermediate gear disposed between the driving gear and the driven gear for transmitting the rotation of the driving gear to the driven gear. In this adjustment mechanism, when the operation part is rotated by the operator, the rotation is transmitted to the threaded rod member via the driving gear, the intermediate gear, and the driven gear, and the threaded rod member is rotated.